Conventional RF transmitting/receiving elements are generally classified into active RF elements which need power supply for driving internal amplifiers, and passive RF elements which do not need power supply. An antenna is taken as an example of an RF transmitting/receiving element. The performance of a passive antenna highly depends on the signal intensity of the RF source. In contrast, an active antenna has a one or two stages of low noise amplifier for amplifying weak RF signals, e.g. GPS signals. Therefore, problems of weak signals in a poor receiver and failed sensitivity can be remedied. In other words, active antennas, when compared with passive antennas, are better for weak signal operations.
However, to drive an amplifier requires a voltage higher than a certain level, so a power supply for the active antenna would be required for the normal operation of the active antenna. Generally, the active antenna power is turned on for link in wireless communication after the active antenna is settled at a proper location and connected to the RF circuit. If power is supplied to the active antenna before the active antenna is well mounted, short circuit might happen to damage the power supply system, or burn down the low noise amplifier in the active antenna. Therefore, it is necessary to operate the active antenna under precise control to avoid unexpected damage.